19035 – Sparse Entrance Detector Array for MR-Linac

Abstract
Sparse detector array for the Elekta MR-Linac to perform both patient-specific and routine machine quality control tasks

Advantages

The Elekta MR-Linac combines a MR-scanner with a linear accelerator capable of delivering a 7 MV photon beam. Conventional measurement devices cannot be used for the routine quality control (QC) of the MR-Linac as they might not be MR compatible and/or they might not satisfy the specific delivery features of the MR-Linac.

In addition, the MR-Linac comes with a software suite that allows for online plan adaption. This means that the treatment plan designed before the first fraction of treatment will be modified everyday while the patient is on the treatment unit couch to take into account any deformation in patient anatomy. For complex radiation therapy delivery techniques, patient-specific QC is usually performed before the first fraction of treatment to assess the agreement between planned and delivered dose. Conventional patient-specific QC measurements will not be possible on the MR-Linac as the patient will be on the couch while the plan is being modified.

The sparse detector array was designed for the QC of the Elekta MR-Linac. It is used specifically to perform:

1. Online patient-specific QC verifications of the modified plans (while the patient is on the couch).

2. Specific routine for the quality control tests of the Elekta MR-Linac (before or after clinical hours).

The Sparse Detector Array consists of a plastic board with 80 linear surface-mount diode arrays. Each linear surface-mount diode array is aligned with the center of one of the 80 MR-Linac MLC leaf pair. The Sparse Detector Array is an entrance radiation detector and it is mounted on the linac head of the MR-Linac in between the linac head and the MR cryostat.

For patient-specific QC, the sparse detector array will be used to measure the radiation beam aperture shape in real-time while a radiation treatment is being delivered to a given patient. The measured field aperture will be compared to the planned field aperture and the treatment will be interrupted if the discrepancy exceed a given tolerance. The sparse detector array will also be used to measure the radiation dose delivered per beam for each patient. The real-time verification of the beam aperture and the dose delivered will eliminate the need for conventional patient-specific QC on the MR-Linac.

The sparse detector array will also be used to perform and automate routine QC tests such as:

1. MLC and jaw position accuracy test

2. Beam output, flatness and symmetry test

These tests will be performed daily before the start of the clinical day and will be completely automated using the proposed technology.

The sparse detector array differs from commercially available QC measurement devices as it is designed specifically for the Elekta MR-Linac requirements. It is MR compatible and it is design to perform both patient-specific and routine machine QC tasks. Its application for real-time patient-specific QC addresses the need for QC of online adapted plans on the MR-Linac. For routine machine QC, the design of the sparse detector array covers the unconventional field size of the MR-Linac and automate important QC tests like beam output verification and MLC and jaw position testing.

Contact Information

Name: Noah Schwartz

Email: Noah.Schwartz@uhnresearch.ca

Phone: 0000000000